This invention relates to an air-conditioning system in which a plurality of indoor units are connected to a single heat source unit and particularly to a refrigerant flow rate control unit so that a multi-room heat pump type air conditioning system is provided for selectively operating the respective indoor units in cooling or heating mode of operation, or wherein cooling can be carried out in one or some indoor units while heating can be concurrently carried out in other indoor units.
FIG. 9 is a general schematic diagram illustrating one example of a conventional heat pump type air-conditioning system. In the figure, reference numeral 1 designates a compressor, 2 is a four-way valve, 3 is a heat source unit side heat exchanger, 4 is an accumulator, 5 is an indoor side heat exchanger, 6 is a first connection pipe, 7 is a second connection pipe, and 9 is a first flow rate controller.
The operation of the above-described conventional air-conditioning system will now be described.
In the cooling operation, a high-temperature, high-pressure refrigerant gas supplied from the compressor 1 flows through the four-way valve 2 and is heat-exchanged with air in the heat source unit side heat exchanger 3, where it is condensed into a liquid. Then, the liquid refrigerant is introduced into the indoor unit through the second connection pipe 7, where it is pressure-reduced by the first flow rate controller 9 and heat-exchanged with air in the indoor side heat exchanger 5 to evaporate into a gas thereby cooling the room.
The refrigerant in the gaseous state is then supplied from the first connection pipe 6 to the compressor 1 through the four-way valve 2 and the accumulator 4 to define a circulating cycle for the cooling operation.
In the heating operation, the high-temperature, high-pressure refrigerant gas supplied from the compressor 1 is flowed into the indoor unit through the four-way valve 2 and the first connection pipe 6 so that it is heat-exchanged with the indoor air in the indoor side heat exchanger 5 to be condensed into liquid thereby heating the room.
The refrigerant thus liquidified is pressure-decreased in the first flow rate controller 9 until it is in the low-pressure, gas-liquid phase state and introduced into the heat source unit side heat exchanger 3 through the second connection pipe 7, where it is heat-exchanged with the air to evaporate into a gaseous state, and is returned to the compressor 1 through the four-way valve 2 and the accumulator 4, whereby a circulating cycle is provided for carrying out the heating operation.
FIG. 10 is a general schematic diagram illustrating another example of a conventional heat pump type air-conditioning system, in which reference numeral 24 designates a low-pressure saturation temperature detection means.
In the above conventional air-conditioning system, when the cooling operation is to be carried out, the compressor 1 is controlled in terms of the capacity so that the detected temperature of the low-pressure saturation temperature detecting means 24 is in coincidence with the predetermined value.
However, in the conventional air-conditioning system, all of the indoor units are coincidentally operated in either cooling or heating mode of operation, so that a problem where an area to be cooled is heated and, contrary, where an area to be heated is cooled.
As an improvement of this, an air conditioning system which allows the concurrent cooling and heating operations as illustrated in FIG. 11.
In FIG. 11, A is a heat source unit, B, C and D are indoor units of the same construction and connected in parallel to each other as described later. E is a junction unit comprising therein a first junction portion, a second flow rate controller, a second junction portion, a gas/liquid separator, a heat exchanger, a third flow rate controller and a fourth flow rate controller.
Reference numeral 20 is a heat source side fan of a variable flow rate for blowing air to the heat source side heat exchanger 3, 6b, 6c and 6d are indoor unit side first connection pipes corresponding to the first connection pipe 6 and connecting the junction unit E to the indoor side heat exchangers 5 of the indoor units B, C and D, respectively, and 7b, 7c and 7d are indoor unit side second connection pipes corresponding to the second connection pipe 7 and connecting the junction unit E to the indoor unit side heat exchangers 5 of the indoor units B, C and D, respectively.
Reference numeral 8 is a three-way switch valve for selectively connecting the indoor unit side first connection pipes 6b, 6c and 6d to either of the first connection pipe 6 or to the second connection pipe 7.
Reference numeral 9 is a first flow rate controller disposed close to the exchanger 5 and connected to the indoor unit side second connection pipes 7b, 7c and 7d and is controlled by the superheating amount at the outlet side of the indoor unit side heat exchanger 5 in the cooling mode of operation, and is controlled by the subcooling amount in the heating mode of operation.
Reference numeral 10 is a first junction portion including three-way valves 8 connected for switching between the indoor unit side first connection pipes 6b, 6c and 6d, the first connection pipe 6 and the second connection pipe 7.
Reference numeral 11 is a second junction portion comprising the indoor unit side second connection pipes 7b, 7c and 7d, and the second connection pipe 7.
Reference numeral 12 designates a gas-liquid separator disposed midpoint in the second connection pipe 7, the gas phase portion thereof being connected to a first opening 8a of the three-way valve 8, the liquid phase portion thereof being connected to the second junction portion 11.
Reference numeral 13 designates a second flow rate controller (an electric expansion valve in this embodiment) connected between the gas-liquid separator 12 and the second junction portion 11.
Reference numeral 14 designates a bypass pipe connecting the second junction portion 11 and the first connection pipe 6, 15 is a third flow rate controller (an electric expansion valve in this embodiment) disposed in the bypass pipe 14, 16a is a second heat exchanging portion disposed downstream of the third flow rate controller 15 inserted in the bypass pipe 14 for the heat-exchange in relation to the junctions of the indoor unit side second connection pipes 7b, 7c and 7d in the second junction portion 11.
16b, 16c and 16d are third heat exchanging portions disposed downstream of the third flow rate controller 15 inserted in the bypass pipe 14 for the heat-exchange in relation to the junctions of the indoor unit side second connection pipes 7b, 7c and 7d in the second junction portion 11.
Reference numeral 19 is a first heat exchanging portion disposed downstream of the third flow rate controller 15 inserted in the bypass pipe 14 and downstream of the second heat exchanging portion 16a for the heat-exchange in relation to the pipe connected between the gas-liquid separator 12 and the second flow rate controller 13, and 17 is a fourth flow rate controller (an electric expansion valve in this embodiment) connected between the second junction portion 11 and the first connection pipe 6.
Reference numeral 32 is a third check valve disposed between the heat source unit side heat exchanger 3 and the second connection pipe 7 for allowing the flow of the refrigerant only from the heat source unit side heat exchanger 3 to the second connection pipe 7.
Reference numeral 33 is a fourth check valve disposed between the four-way valve 2 of the heat source unit A and the first connection pipe 6 for allowing the flow of the refrigerant only from the first connection pipe 6 to the four-way valve 2.
Reference numeral 34 is a fifth check valve disposed between the four-way valve 2 and the second connection pipe 7 for allowing the flow of the refrigerant only from the four-way valve 2 to the second connection pipe 7.
Reference numeral 35 is a sixth check valve disposed between the heat source unit side heat exchanger 3 and the first connection pipe 7 for allowing the flow of the refrigerant only from the first connection pipe 6 to the heat source unit side heat exchanger 3.
The above-described third, fourth, fifth and sixth check valves 32, 33, 34 and 35, respectively, constitutes a flow path change-over unit 40.
Reference numeral 21 designates a takeoff pipe connected at one end thereof to the liquid outlet pipe of the heat source unit side heat exchanger 3 and to the inlet pipe of the accumulator 4, 22 is a throttle disposed in the takeoff pipe 21, and 23 designates a second temperature detection means disposed between the throttle 22 and the inlet pipe of the accumulator of the takeoff pipe 21.
The conventional air-conditioning system capable of a concurrent heating and cooling operation has the above-described construction. Accordingly, when only the cooling operation is being carried out, the high-temperature, high-pressure refrigerant gas supplied from the compressor 1 flows through the four-way valve 2 and is condensed into a liquid in the heat source unit side heat exchanger 3 with the air supplied from the variable capacity heat source unit side fan 20. Then, the liquid refrigerant is introduced into the respective indoor units B, C and D through the third check valve 32, the second connection pipe 7, the gas-liquid separator 12, the second flow rate controller 13, the second junction portion 11 and through the indoor unit side second connection pipes 7b, 7c and 7d.
The refrigerant introduced into the indoor units B, C and D is decreased in pressure by the first flow rate controller 9 controlled by the superheating amount at the outlet of the indoor unit side heat exchanger 5, where it is heat-exchanged in the indoor unit side heat exchanger 5 with the indoor air to be evaporated into a gas to cool the room.
The gaseous refrigerant is flowed through the indoor unit side first connection pipes 6b, 6c and 6d, the three-way change-over valve 8, the first junction portion 10, the first connection pipe 6, the fourth check valve 33, the four-way valve 2 of the heat source unit and the accumulator 4 into the compressor 1 to define a circulating cycle for the cooling operation.
At this time, the first opening 8a of the three-way change-over valve 8 is closed while the second opening 8b and the third opening 8c are opened. At this time, the first connection pipe 6 is at a low pressure and the second connection pipe 7 is at a high pressure, so that the refrigerant inevitably flows toward the third check valve 32 and the fourth check valve 33.
Also, in this cycle, one portion of the refrigerant that passes through the second flow rate controller 13 is introduced into the bypass pipe 14 and is press-reduced in the third flow rate controller 15 and heat-exchanged in the third heat exchanging portions 16b, 16c and 16d in relation to the indoor unit side second connection pipes 7b, 7c and 7d of the second junction portion 11. Thereafter, the heat-exchanging is carried out in the second heat exchanging portion 16a in relation to the indoor unit side second connection pipes 7b, 7c and 7d of the second junction portion 11, and a further heat-exchanging is carried out in the first heat exchanging portion 19 in relation to the refrigerant flowing into the second flow rate controller 13 to evaporate the refrigerant, which then is supplied to the first connection pipe 6 and the fourth check valve 33 to be returned into the compressor 1 through the four-way valve 2 of the heat source unit and the accumulator 4.
On the other hand, the refrigerant within the second junction portion 11 which is heat-exchanged and cooled at the first, second and third heat-exchanging portions 19, 16a, 16b, 16c and 16d and is introduced into the indoor units B, C and D to be cooled.
In the mode of operation in which cooling is mainly carried out in the concurrent cooling and heating operations, the refrigerant gas supplied from the compressor 1 is flowed into the heat source unit side heat exchanger 3 through the four-way valve 2, where it is heat-exchanged in relation to the air supplied by the variable capacity heat source unit side fan 20 to become a high-temperature and high-pressure gas-liquid phase. At this time, the pressure obtained on the basis of the saturation temperature detected by the second temperature detecting means 23 is used to adjust the air flow rate of the heat source unit side fan 20 and the capacity of the compressor 1.
Thereafter, this refrigerant in the high-temperature, high-pressure gas-liquid phase state is supplied to the gas-liquid separator 12 of the junction unit E through the third check valve 32 and the second connection pipe 7.
Then, the refrigerant is separated into the gaseous refrigerant and the liquid refrigerant, the separated gaseous refrigerant is introduced into the indoor unit D to be heated through the first junction portion 10, the three-way valve 8 and the indoor unit side first connection pipe 6d, where it is heat-exchanged in relation to the indoor air in the indoor unit side heat exchanger 5 to be condensed into a liquid to heat the room.
The refrigerant is then controlled by the subcooling amount at the outlet of the indoor unit side heat exchanger 5, flows through the substantially fully opened first flow rate controller 9 where it is slightly pressure-decreased and enters into the second junction portion 11. On the other hand, the liquid refrigerant is supplied to the second junction portion 11 through the second flow rate controller 13, where it is combined with the refrigerant which passes through the indoor unit D to be heated and introduced into each indoor units B and C through the indoor unit side second connection pipes 7b and 7c. The refrigerant flowed into the respective indoor units B and C is pressure-reduced by the first flow rate controller 9 controlled by the superheating amount at the outlet of the indoor unit side heat exchangers B and C and is heat-exchanged in relation to the indoor air to evaporate into vapor to cool the room.
The vaporized refrigerant then flows through a circulating cycle of the indoor unit side first connection pipes 6b and 6c, the three-way valve 8 and the first junction portion 10 to be suctioned into the compressor 1 through the first connection pipe 6, the fourth check valve 33, the four-way valve 2 of the heat source unit and the accumulator 4, thereby to carry out the cooling-dominant operation.
The conventional air-conditioning system constructed as above-described has a problem in that, a disturbance of the refrigerant cycle is generated due to the variation in pressure of the refrigeration cycle and a stable detection of the low-pressure saturation temperature in the heat source unit cannot be achieved due to the variation of the indoor cooling load when the operation is cooling only or due to the variation of the indoor cooling load or heating load when the operation is cooling-dominant. When the operation is cooling-dominant, the refrigerant which passed through the heat source unit side heat exchanger becomes vapor-liquid phase state, preventing a stable detection of the saturation temperature of the refrigerant. Alternatively, when the number of indoor units in the cooling operational mode, when the units are started for cooling operation after a long period of stoppage or when the cooling operation is started immediately after heating operation, a large amount of liquid refrigerant stays in the accumulator or the like, so that a vapor-liquid two-phase state due to lack of refrigerant takes place at the inlet of the first flow rate controller 9, increasing the flow path resistance of the first flow rate controller 9, which causes the decrease in refrigerant pressure, the decrease in the refrigerant circulating amount and the decrease in the low pressure saturation temperature whereby the cooling capacity is disadvantageously decreased and the heating and cooling cannot be selectively carried out by each indoor unit and a stable concurrent cooling and heating operation in which some of the indoor units carry out cooling and some other of the indoor units carry out heating.
In particular, when the air-conditioning system is installed in a large-scale building, the air-conditioning load is significantly different between the interior portion and the perimeter portion, and between the general offices and the OA (office automated) room such as a computer room.